Actually i find the CCleaner registry cleaner (awful redundancy here xD) to be really good. i mean, it doesnt mess with weird registry entries and stuff.
But of course this doesn't mean anything to the average "click, next, next, next, finish, close" type of users who don't read what they're about to do or delete or whatever. You have to really know what you're doing
when it comes to Registry Cleaners, because deleting something that you shouldn't be deleting, could lead you into some trouble.
So i'd say, don't use the registry cleaner from CCleaner unless you know what you're doing, otherwise you'll be regretting it when you have an unrecoverable issue
Better safe than sorry